Even earlier than floor treatment, the looks and surface high quality of extruded aluminium profiles is completely passable for a lot of functions. Because of good corrosion resistance, floor treatment isn’t mandatory merely to offer corrosion safety. Nevertheless, there are lots of different causes for treating the surfaces of profiles. Examples of attributes that may be modified by floor remedy embrace:
– surface construction
– color
– corrosion resistance
– hardness
– wear resistance
– reflectivity
– electrical insulation

Surfaces don’t at all times want remedy after extrusion. Load-bearing buildings and machine elements are examples of merchandise the place the surface high quality is passable with none treatment.

Profile design

Strains and extrusion stripes that will be noticeable on seen surfaces can simply be hidden utilizing ornament. Such patterns or optical results are an integral a part of the profile resolution created on the design stage.

Mechanical floor remedy

Grinding

Grinding is likely one of the strategies used for bettering floor high quality. The method leaves a tremendous striation within the route of grinding. The resultant floor could be “very tremendous”, “medium” or “coarse”. Grinding is mostly used for furnishing and inside design merchandise. Floor surfaces are sometimes anodised. Grinding earlier than portray can additional enhance the floor end.

Sharpening

Sharpening smoothes the floor. High quality and gloss are decided by buyer specs. Polished surfaces usually go on to be anodised. To attain a high-gloss end, sprucing is adopted by brilliant anodising.

Tumbling (barrel sharpening)

Tumbling is principally used for deburring. Decided by the sharpening medium used within the drum, surfaces vary all the way in which from matt to gloss.

Anodising

Anodising, some of the widespread floor remedies, is used to (amongst different issues):
– preserve a product’s “as-new” look.
– improve corrosion resistance.
– create a mud repellent floor that satisfies stringent hygiene necessities.
– create an ornamental floor with sturdy color and gloss.
– create a “touch-friendly” floor.
– create function-specific surfaces, for instance, slip surfaces, abrasion-resistant surfaces to be used in machine components, and many others.
– give surfaces an electrically insulating coating.
– present a base for the applying of adhesives or printing inks.

The anodising course of

There are usually 4 phases within the course of: pre-treatment, anodising, colouring (the place required) and sealing. Essentially the most frequent kind of anodising is pure anodising. The electrolytic course of takes place as soon as the steel floor has acquired the suitable mechanical or chemical pre-treatment and has been completely cleaned.

The profile is linked to a direct present supply and turns into the anode (therefore anodising). An electrolytic cell is shaped. Dilute sulphuric acid at room temperature is often used because the electrolyte. Throughout electrolysis, the floor of the steel is oxidised. The method continues till the specified layer thickness (normally 5 – 25 μm) is reached.

Sealing

The oxide layer comprises numerous pores, approx. 1011/cm2 (i.e. round 100 billion). The diameter of the pores is between 120 and 330 Å. To acquire an impermeable floor, the pores need to be sealed. Sealing is achieved by treating the floor in de-ionised water at 95 – 98°C. This modifications the aluminium oxide into bohemite, the attendant enhance in quantity closing the pores.

The anodic oxide layer has good corrosion resistance in most environments. With the proviso that the floor is cleaned, anodised profiles are nearly maintenance-free. The floor cleans simply in each water with just a little impartial detergent and in white spirits. Though solvents don’t have an effect on aluminium, sturdy alkaline options must be averted.

Resistance to corrosion, discoloration and abrasion will increase with layer thickness. Suggestions for appropriate thicknesses are given within the desk above.

Because the anodic oxide layer has poor chilly formability, forming ought to happen earlier than anodising. Reducing and drilling may be carried out after anodising however the uncovered surfaces will, after all, be untreated. Welding is to be carried out earlier than anodising.

Properties of anodised aluminium

Corrosion resistance is superb, particularly the place pH is between four and 9. In touch with strongly alkaline substances, surfaces can stain and be broken. Thus, it must be borne in thoughts that aluminium must be protected in opposition to lime, cement and gypsum (e.g. on constructing websites). Seen surfaces will be protected utilizing tape.

The hardness of the oxide layer will depend on the anodising course of used. Usually, the layer is tougher than glass and as laborious as corundum. The oxide layer is clear. Whether or not pure or colored, its look will depend on the viewing angle.

At temperatures above 100°C, fantastic cracks kind within the oxide layer. From an aesthetic perspective, this can be an undesirable impact.

The reflectivity of brilliant etched aluminium is excessive. The gloss worth is 90 items (ISO 7599, 60° viewing angle). This decreases barely with anodising. The oxide layer is an electrical insulator. A sealed, 15 μm oxide layer has a breakdown voltage of 500 – 600 V. An anodised profile may be recycled with no pre-treatment. Earlier than remelting, painted profiles should first have the paint eliminated.

Portray

Portray gives a limitless selection of colors and superb color matching (repeatability). Powder coating is now simply essentially the most widespread technique of portray aluminium profiles.

To make sure the best adhesion for the paint, it will be important that pre-treatment, paint software and subsequent curing are all carried out appropriately. As most adhesion and sturdiness are prime objectives, pre-treatment is of essential significance. Pre-treatment usually contains degreasing and pickling of the floor, adopted by a chemical remedy.

The chemical therapy (chrome-free or chrome-based) offers good adhesion and efficient corrosion resistance. The chrome-free titanium primarily based course of is GSB accredited and is now our commonplace methodology. It has undergone in depth testing.

Rinse water from the chromating course of is handled in environment friendly cleansing vegetation. The sludge is drawn off and despatched away for acceptable disposal. Pre-treatment is identical for each powder coating and moist portray.

Powder coating

Broadly talking, there are completely no limits to the selection of color. Powder coatings are utilized and cured with out solvents. This provides a very good work setting and has no adverse impression on the exterior setting.

In a moist coating plant, half the paint is misplaced by way of evaporation and the waste concerned in over-spraying. In a contemporary powder coating plant, as much as 98% of the powder is used. Powder that doesn’t adhere to the product is recirculated through a reclamation system.

Powder coating qualities

The prime qualities of powder coating and powder coats are:
– No threat of working or blistering.
– Excessive repeatability.
– Powder coatings face up to knocks and abrasion much better than
moist paint coatings.
– Good formability (e.g. could be fashioned after coating).
– Appropriate for outside use – good resistance to UV and corrosion.

Coating thickness is often 60 – 140 μm. In some designs, the thickness of the coating needs to be considered when figuring out profile dimensions and tolerances.

Display screen printing

Display printing (previously silk-screen printing) is an historical printing technique. The unique design is reproduced on a clear movie that’s then positioned on a fine-meshed display screen (often nylon these days). That is then uncovered and developed photographically. The display is subsequent fitted right into a body. Both manually or routinely, a squeegee is dragged alongside the display to switch the design onto the printing floor.

Tampon printing

Tampon printing is a way that makes it potential to make use of display screen printing on each concave and convex surfaces.

Pure and color anodising on the identical profile

Utilizing display screen printing, a profile’s surfaces can mix pure anodising and colouring. Anodising is interrupted when the oxide layer has fashioned. The profile areas that aren’t to be printed are then coated with a particular masking ink. After printing, the profile is sealed within the regular manner.

Unanodised surfaces on anodised profiles

A masking approach can be used when elements of a profile are to emerge unanodised from the anodising course of. This preserves the floor’s electrical and thermal conductivity (the anodic oxide layer is insulating).

Perform particular surfaces

A function-specific floor is outlined as one the place sure function-related properties are of crucial significance.

Slip, friction and sealing surfaces

Right here, the floor roughness (i.e. the Ra values, axially and radially) is of the utmost significance. Cylinder tubes are an instance. Direct from the press, tubes may be delivered the place the insides have Ra values as little as zero.6 axially and 1.2 radially. The Ra values can, after all, be additional improved by machining.

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